In an image sensor, in particular, a. CMOS (Complementary Metal-Oxide Semiconductor) image sensor, each frame is constituted by N×M unit pixels. When the image sensor is operating in a low-resolution mode, the outputs of only some of the unit pixels, not all the unit pixels, are sent.
The low-resolution mode in which the image sensor operates includes a sub-sampling mode and a binning mode.
For example, when the image sensor is operating with a resolution which is a quarter of the full resolution, it should suffice that only the outputs of the N/2×M/2 pixels from among all the N×M pixels are sent. In the sub-sampling mode, an operation is performed such that the outputs of the N/2 row pixels are sent, and the outputs of the remaining N/2 row pixels are not sent. Meanwhile, in the binning mode, the outputs of pixels of the same color in two adjacent pixels are added and output as a single pixel output value. In the binning mode, there is no pixel output value to be discarded, so that an image is formed using all the pixel output values, thereby obtaining a high-quality image as compared to the sub-sampling mode.
FIG. 1 illustrates the sub-sampling mode and the binning mode.
As illustrated in FIG. 1, in the sub-sampling mode, only pixel information of the pixels in the first and second rows from among the pixels in the four total rows of the pixel array 10 can be output, for example, only pixel information of Gb41-B41-Gb42-B42-Gb43-B43 and R31-Gr31-R32-Gr32-R33-Gr33 can be output.
In order to minimize noise for the pixel information to be read in the sub-sampling mode, the binning mode may be executed in which the read pixel information and unread pixel information of the pixels in the third and fourth rows, for example, pixel information of Gb21-B21-Gb22-B22-Gb23-B23 and R11-Gr11-R12-Gr12-R13-Gr13 are added (averaged).
At this time, in the sub-sampling mode and the binning mode of the whole pixel array, the pixel information of Gb41-B41-Gb42-B42-Gb43-B43 of the first row is temporarily stored in a line memory 12 and added to the pixel information of Gb21-B21-Gb22-B22-Gb23-B23 of the third row having the same color arrangement as the pixel information of the first row, and averaging is performed. Next, the pixel information of R31-Gr31-R32-Gr32-R33-Gr33 of the second row is temporarily stored in the line memory 12 and added to the pixel information of R11-Gr11-R12-Gr12-R13-Gr13 of the fourth row having the same color arrangement as the pixel information of the second row, and averaging is performed.
In the image sensor of the related art, since it is necessary to store previous information so as to obtain an average in the sub-sampling mode and the binning mode, there is a need for the additional line memory 12, and it is necessary to separately read pixel information of two rows for obtaining an average two times.
This leads to an increase in a whole memory area and a decrease in the sensing timing of the pixels to be equal to or lower than 50%.